Vacuum may be used to operate or to assist in the operation of various devices of a vehicle. For example, vacuum may be used to assist a driver applying vehicle brakes. Further, vacuum may be used to adjust the position of a turbocharger waste gate or a turbocharger vane position. Vacuum is often obtained from an engine intake manifold in normally aspirated engines because the intake manifold pressure is often at a pressure lower than atmospheric pressure. However, in boosted engines where intake manifold pressures are often at pressures greater than atmospheric pressure, intake manifold vacuum may replaced or augmented with vacuum from a pump. In systems that rely on intake manifold vacuum and/or pump vacuum, pressure controlled check valves may be used to control vacuum of a reservoir that assists actuator operation. For example, if engine intake manifold pressure is low, air may be drawn from a vacuum reservoir to the engine intake manifold via a pressure controlled check valve. However, if engine intake manifold pressure is high, the pressure controlled check valve may limit air flow from the intake manifold to the vacuum reservoir. In this way, vacuum that assists actuator operation of a vehicle system may be controlled.
Pressure controlled check valves have known operating characteristics and are inexpensive. However, pressure controlled check valves may open or close during engine operating conditions when it may not be desirable to do so. For example, if an engine is operating at a low load condition and an opening area of the air intake passage throttle is small, vacuum in the engine air intake manifold may cause a pressure controlled valve to open such that air flow to the engine increases beyond a desired amount. As a result, engine spark may be retarded so that the desired engine torque is provided. However, increasing the engine spark retard can decrease engine efficiency and increase engine fuel consumption.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: operating an engine at a condition where a intake throttle is substantially closed; and closing a valve to limit engine air flow from a vacuum reservoir to the engine intake manifold when a pressure in the engine intake manifold is less than a pressure in the vacuum reservoir.
By closing a valve between a vehicle vacuum reservoir and an engine intake manifold, it may be possible to reduce fuel consumption and provide system vacuum. In particular, a valve between an engine intake manifold and a vacuum reservoir may be closed to limit air flow to the engine. Thus, fuel may be conserved because additional fuel may not have to be delivered to the engine to keep engine exhaust gases substantially stoichiometric. Further, a vacuum pump can provide vacuum to vehicle systems while the intake manifold is isolated from the vacuum reservoir via the valve. In this way, it is possible to reduce engine fuel consumption and provide vacuum to a vehicle system vacuum reservoir.
The present description may provide several advantages. For example, the approach may improve engine fuel economy. Further, the approach can provide additional system flexibility. Further still, the approach may provide improved vacuum control during some conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.